1. Field of the Invention
This invention relates to an apparatus for recognizing the shape of a road which can be mounted on, for example, a vehicle. In addition, this invention relates to an on-vehicle apparatus for detecting a preceding vehicle. Furthermore, this invention relates to a recording medium which stores a computer program for recognizing the shape of a road.
2. Description of the Related Art
There is an on-vehicle apparatus for controlling the present vehicle to automatically maintain the distance between the present vehicle and a preceding vehicle in a safe range. In general, such an inter-vehicle distance control apparatus contains a radar device for measuring the distance to a preceding vehicle from the present vehicle and the speed of the preceding vehicle relative to the present vehicle. In the inter-vehicle distance control apparatus, an objective preceding vehicle for inter-vehicle distance control is selected from among candidate preceding vehicles detected via the radar device. It is desirable to accurately determine an objective preceding vehicle even when the present vehicle is traveling along a curved road. The recognition of a road shape is effective in accurate determination of an objective preceding vehicle.
Japanese patent application publication number 8-249598 discloses an on-vehicle apparatus for sensing delineators and recognizing a road shape from information about the sensed delineators. The apparatus in Japanese application 8-249598 emits a forward electromagnetic wave beam from the body of the vehicle, and controls the forward electromagnetic wave beam to periodically scan a given angular region (a detection area) in front of the body of the vehicle. In the case where an object exists in the given angular region (the detection area), the forward electromagnetic wave beam encounters the object before being at least partially reflected thereby. A portion of the reflected electromagnetic wave beam returns to the apparatus as an echo electromagnetic wave beam. The apparatus detects the object in response to the echo electromagnetic wave beam. Specifically, the apparatus calculates the distance to the object from the time interval between the moment of emission of the forward electromagnetic wave beam and the moment of reception of the related echo electromagnetic wave beam. In addition, the apparatus calculates the direction of the object relative to the vehicle.
The apparatus in Japanese application 8-249598 decides whether each detected object is a delineator on a right-hand road side or a delineator on a left-hand road side in response to the horizontal variation in the position of the object relative to the vehicle. Decided delineators on a right-hand road side are linked by lines, and the set of the lines is recognized as a right-hand road edge. Similarly, decided delineators on a left-hand road side are linked by lines, and the set of the lines is recognized as a left-hand road edge. The apparatus in Japanese application 8-249598 has a chance of erroneously detecting road edges in the case where the vehicle is traveling along a road provided with three or more rows of cat""s-eyes.
Japanese patent application publication number 10-239436 discloses an apparatus for detecting the vehicle-to-vehicle distance. The apparatus in Japanese application 10-239436 emits a forward laser beam, and controls the forward laser beam to periodically scan a given angular region in front of the body of the present vehicle. The apparatus in Japanese application 10-239436 detects objects in the given angular range from return laser beams coming therefrom. Specifically, the apparatus detects the positions of the objects relative to the present vehicle. In more detail, the apparatus detects the distances to the objects and the directions (the angular positions) of the objects relative to the present vehicle. The detected objects include reflectors on the right-hand and left-hand sides of the road. In the apparatus of Japanese application 10-239436, the shape of the road is recognized from the loci (trajectories) of detected reflectors on the road sides. In addition, the range of the lane along which the present vehicle is traveling is calculated on the basis of the recognized road shape. Furthermore, a preceding vehicle is detected on the basis of the object positions relative to the present vehicle and the calculated range of the lane.
Japanese patent application publication number 6-68398 discloses an on-vehicle apparatus for detecting a road. The apparatus in Japanese application 6-68398 includes a radar device for emitting a forward electromagnetic wave beam, and controls the forward electromagnetic wave beam to periodically scan a given angular region in front of the body of the present vehicle. The radar device detects objects in the given angular range from return electromagnetic wave beams coming therefrom. Specifically, the radar device detects the positions of the objects relative to the present vehicle. The detected objects include reflectors on the right-hand and left-hand sides of the road, and reflectors on preceding vehicles. The apparatus of Japanese application 6-68398 estimates the shape of the road from at least one of 1) the positions of detected reflectors relative to the present vehicle and 2) the horizontal variations in the positions of the detected reflectors.
It is a first object of this invention to provide an improved apparatus for recognizing the shape of a road.
It is a second object of this invention to provide an improved on-vehicle apparatus for detecting a preceding vehicle.
It is a third object of this invention to provide a recording medium which stores an improved computer program for recognizing the shape of a road.
A first aspect of this invention provides a road-shape recognition apparatus comprising a radar device for emitting a detection wave ahead of a vehicle, and detecting objects in response to echoes of the emitted detection wave; reflector detecting means for detecting reflectors among the objects detected by the radar device, the reflectors being located along a road; reflector-row extracting means for, in cases where there are a plurality of rows of the reflectors detected by the reflector detecting means in one side of the vehicle, extracting one from among the reflector rows; and road-shape recognizing means for recognizing a shape of the road on the basis of the reflector row extracted by the reflector-row extracting means.
A second aspect of this invention is based on the first aspect thereof, and provides a road-shape recognition apparatus wherein the reflector-row extracting means comprises means for extracting one, which exists in a specified region with respect to the vehicle in a width-wise direction of the vehicle, from among the reflector rows.
A third aspect of this invention is based on the second aspect thereof, and provides a road-shape recognition apparatus wherein the reflector-row extracting means comprises means for setting the specified region in accordance with a width of a lane along which the vehicle is traveling.
A fourth aspect of this invention is based on the second aspect thereof, and provides a road-shape recognition apparatus wherein the reflector-row extracting means comprises position estimating means for estimating positions, in the width-wise direction of the vehicle, of the reflectors detected by the reflector detecting means which occur after a lapse of an arbitrary time; minimum position detecting means for detecting, among the positions estimated by the position estimating means, a minimum position corresponding to a position nearest to the vehicle; and means for setting the specified region on the basis of the minimum position detected by the minimum position detecting means.
A fifth aspect of this invention is based on the second aspect thereof, and provides a road-shape recognition apparatus wherein the reflector-row extracting means comprises position estimating means for estimating positions, in the width-wise direction of the vehicle, of the reflectors detected by the reflector detecting means which occur after a lapse of an arbitrary time; determining means for determining whether or not there are a plurality of the positions estimated by the position estimating means; lane-width calculating means for, in cases where the determining means determines that there are a plurality of the positions estimated by the position estimating means, calculating a lane width on the basis of an interval between the estimated positions; and means for setting the specified region on the basis of the lane width calculated by the lane-width calculating means.
A sixth aspect of this invention is based on the first aspect thereof, and provides a road-shape recognition apparatus further comprising at least one of 1) a steering sensor for detecting a steering angle of the vehicle and 2) a yaw rate sensor for detecting a yaw rate of the vehicle; curvature-radius calculating means for calculating a curvature radius of a course, along which the vehicle is traveling, from at least one of 1) the steering angle detected by the steering sensor and 2) the yaw rate detected by the yaw rate sensor; position converting means for converting positions, in a width-wise direction of the vehicle, of the reflectors detected by the reflector detecting means into positions in the width-wise direction of the vehicle which occur on the assumption that the vehicle is traveling along a straight road; and means provided in the reflector-row extracting means for extracting one, which exists in a specified region with respect to the vehicle in the width-wise direction of the vehicle, from among the reflector rows in response to the positions resulting from the conversion by the position converting means.
A seventh aspect of this invention is based on the fourth aspect thereof, and provides a road-shape recognition apparatus wherein the road-shape recognizing means comprises means for recognizing the shape of the road on the basis of the reflector row extracted by the reflector-row extracting means and the positions estimated by the position estimating means.
An eighth aspect of this invention is based on the fourth aspect thereof, and provides a road-shape recognition apparatus wherein the position estimating means comprises means for estimating the positions, in the width-wise direction of the vehicle, of the reflectors detected by the reflector detecting means which occur after the lapse of the arbitrary time on the basis of relative speeds between the vehicle and the reflectors detected by the reflector detecting means.
A ninth aspect of this invention is based on the first aspect thereof, and provides a road-shape recognition apparatus wherein the reflector detecting means comprises means for detecting the reflectors among the objects detected by the radar device on the basis of relative speeds between the vehicle and the objects and sizes of the objects.
A tenth aspect of this invention provides a recording medium storing a computer program for road-shape recognition which comprises the steps of detecting reflectors among detected objects, the reflectors being located along a road; in cases where there are a plurality of rows of the detected reflectors in one side of a vehicle, extracting one from among the reflector rows; and recognizing a shape of the road on the basis of the extracted reflector row.
An eleventh aspect of this invention provides a preceding-vehicle detection apparatus for a subject vehicle. The apparatus comprises the road-shape recognition apparatus of the first aspect of this invention; relative position detecting means for detecting positions of the objects detected by the radar device relative to the subject vehicle; lane-sameness probability calculating means for calculating a probability for each of the objects that the object and the subject vehicle are on a same lane on the basis of the road shape recognized by the road-shape recognizing means and the relative position detected by the relative position detecting means; and preceding-vehicle detecting means for detecting a preceding vehicle with respect to the subject vehicle among the objects in response to the probabilities calculated by the lane-sameness probability calculating means.